We made a modification to the delay circuit so to incorporate a 5V relay, same as the others so not to complicate the BOM. The original delay circuit was 12V and it exploited the 6-9V E,B breakdown effect of a first reversed NPN. We are charging up to the 0.7V Vbe of just one transistor now (the one that pulls the relay coil) with 47k to 220uF for about 1.5 to 2 sec delay. The 7805 will need a small sink due to the bigger drop across it than being a 7812. It works without any on thump noise or offset as reported. After xaudiox uses it just a bit more with no glitches, he will be ready to send the files to the pcb maker. We are practically ready.
Salas said:
My suggestion is to use TQ2-12V for those that still have to buy the relays. That would technically be the most optimal and simple solution. Less voltage drop on the reg and the muting circuit will work as designed. Two birds with one stone.
This is a small error which is normal when designing stuff. Just skip the 5 V relays.
IMO the double bridges have more disadvantages than advantages. Please consider using a single bridge with a 2 x 12v transformer just like La Ode did.
Both can be done on same board. For those having the 5V relay, they can jumper the first NPN, use 7805 with sink, and 220uF delay cap. I prefer the 12V original which gives about 5sec delay having to rise to about 8V with 47k to 47uF. The double bridge is doing an OR function between secondaries that leads nearer to double mono with one trafo, and real double mono with two trafos, but it rectifies to about X1.2 the VAC. But 2X15VAC isn't hard to find either. Its up to you guys, me I was OK with single bridge and 2X12V as per original. As I have seen during the course of the thread, double bridge was a request from people aspiring to double mono.
Salas said:
Sorry but this is not according the definition of "double mono" depending on how double mono is defined. For double mono the shunt supplies should have to be doubled so separate shunts regs per channel both negative and positive. Furthermore 2 separate transformers with 2 x 12 V windings or one transformer with 4 x 12 V windings would have to be used. "Double mono" is like having a separate amp with its own power supply per channel.
Just one transformer could be used to save on costs but it would not be double mono anymore ( but with better separation than only one set of regs anyway ). We called it "pseudo double mono".
In this case one winding is used entirely for the positive supply for both channels and one winding is used for the negative supply of both channels.
AFAIK using 2 bridges as used here is only beneficial for better loading of the transformer like with power amps. With 40 mA load I would not have worries about that...
Off topic: when searching for the theory of Graetz bridges I stumbled upon this:
http://isa.umh.es/temas/micros/doc/datasheets/L6210.pdf
Never knew they existed in this form and they're Schottky too.
http://isa.umh.es/temas/micros/doc/datasheets/L6210.pdf
Never knew they existed in this form and they're Schottky too.
Maybe when xaudiox still is working on the layout he could add pads for using MUR diodes ( in TO220 case ) as well. Could you add this possibility xaudiox ?
Salas, do I understand correctly that you prefer 4 diodes too for the bridge ? I think the design will be cheaper, technically just as good and the layout would be nicer on that area of the PCB too. The area that could be won can be used for some extra diodes to drop the voltage to the 7805 for those that use 5V relays.
Salas, do I understand correctly that you prefer 4 diodes too for the bridge ? I think the design will be cheaper, technically just as good and the layout would be nicer on that area of the PCB too. The area that could be won can be used for some extra diodes to drop the voltage to the 7805 for those that use 5V relays.
I don't know, it was a surprise to find out:
a. they exist in DIL16 packages too.
b. even two schottky bridges exist in one DIL16 case.
Being a Schottky it will probably be slightly better than the standard 1N4004 bridges despite the fact they're fast recovery. Just a guess.
BTW "Old" is a parameter that does not count in audio
Just ask the tube guys.
OK, back to the topic...
a. they exist in DIL16 packages too.
b. even two schottky bridges exist in one DIL16 case.
Being a Schottky it will probably be slightly better than the standard 1N4004 bridges despite the fact they're fast recovery. Just a guess.
BTW "Old" is a parameter that does not count in audio
Just ask the tube guys.OK, back to the topic...